Make support interface pattern const
Make support interface pattern const

It doesn't change here and it shouldn't change.

Contributes to issue CURA-3491.

alephobjects/CuraEngine,ROBO3D/CuraEngine,alephobjects/CuraEngine,alephobjects/CuraEngine,Ultimaker/CuraEngine,ROBO3D/CuraEngine,Ultimaker/CuraEngine,ROBO3D/CuraEngine